Aramid thin sheet material and electrical/electronic parts using the same

ABSTRACT

The invention provides an aramid thin sheet material comprising two components of aramid staple fibers and fibrillated aramid, or said two components and aramid fibrid, in particular, characterized by satisfying both of the following expressions (1) and (2): 
 
[internal resistance] (μm)≦250 (μm)  expression (1) 
 
[Oken-type gas permeability] (sec/100 cm 3 )≧0.5 (sec/100 cm 3 )  expression (2) 
 
wherein the [internal resistance] is a resistance value calculated by the following expression (3):  
                           [     internal   ⁢           ⁢   resistance     ⁢           ]     ⁢     (     μ   ⁢           ⁢   m     )       =               [             electrical   ⁢           ⁢   conductivity     ⁢                       of   ⁢           ⁢   electrolyic   ⁢           ⁢   solution           ]             [                 electrical   ⁢           ⁢   conductivity               of   ⁢           ⁢   electrolytic                       solution   ⁢     -     ⁢   injected     ⁢                       thin   ⁢           ⁢   sheet   ⁢           ⁢   material           ]       ×     [           thickness   ⁢                         of   ⁢           ⁢   the     ⁢                               ⁢   thinsheet                       ⁢   material           ]     ⁢       (     μ   ⁢           ⁢   m     )     .             expression   ⁢           ⁢     (   3   )

TECHNICAL FIELD

This invention relates to aramid thin sheet material useful as separators for separating conductive members in electrical/electronic parts to allow passage of ionic species such as electrolyte or ion; and also to electrical/electronic parts using the separators. In particular, the invention relates to aramid thin sheet material useful for separator panels between electrodes in condensers, capacitors, batteries and the like which use lithium ion, sodium ion, ammonium ion, hydrogen ion and the like as a carrier of electric current.

BACKGROUND ART

As symbolized by the recent progress in portable communication devices or high-speed information processors, reduction in size and weight and advance in technical performance of electronic instruments are splendid. Above all, more expectation is placed on small size, light weight, and higher capacity and performance electric batteries and condensers which can withstand storage over prolonged period. Their application range is being broadened and developments of parts for their use are under rapid progress. Correspondingly, there are growing needs for developing improved technology and quality for such members as separators which serve as partition plates between electrodes.

Among various properties required for separators, the following three are recognized to be particularly important:

1) that they exhibit good electrical conductivity in the state of holding an electrolyte;

2) that they have high inter-electrodes shielding performance; and

3) that they have mechanical strength.

Conventionally, as separators in electrical/electronic parts, porous sheeting formed of polyolefin polymer such as polyethylene or polypropylene (cf. JP Sho63(1988)-273651A); non-woven fabric in which polyolefin polymer fibers such as of polyethylene or polypropylene are made into sheet (cf. JP2001-11761A); non-woven fabric in which nylon fibers are made into sheet (cf. JP Sho58(1983)-147956A) have been widely used. Such separators are used in batteries in the form of mono-layer, multiple layers or wound-up roll.

Furthermore, micropores are formed on the surfaces of members used in electrodes by

1) etching aluminum foil electrodes for aluminum electrolytic condensers, or

2) using activated carbon as electrodes in electric double layer capacitors,

to increase their surface areas to impart high capacity thereto.

DISCLOSURE OF THE INVENTION

Such micro-porous sheeting and non-woven fabrics possess favorable physical properties for the separator, but do not necessarily fully meet recent demands for condensers, capacitors or batteries of still higher capacity and power output required for electric cars.

A separator for use in electrical/electronic parts for condensers, capacitors, batteries and the like which are required to have high capacity and large power output must simultaneously satisfy the following five property requirements:

1) good electrical conductivity in the state of holding an electrolyte,

2) high inter-electrodes shielding ability,

3) high mechanical strength,

4) chemical and electrochemical stability (heat resistance), and

5) capability to withstand high temperature drying (heat resistance).

In particular, inter-electrodes shielding ability and heat resistance are considered to be extremely important, for

1) preventing short-circuit between conductive members in electrical/electronic parts using high-intensity electric current with high-capacity electrodes filled at high density, such as condensers, capacitors and batteries as drive power source of, for example, electric cars, and

2) thoroughly drying moisture in micropores in electrodes such as of aluminum foil or activated carbon, during manufacturing steps of electrical/electronic parts.

Under the circumstances, the present inventors have engaged in concentrative studies with the view to develop a material for highly heat resistant separators which withstand high-intensity electric current necessitated for higher capacity and large power output and also are durable under high-temperature drying during their manufacturing steps, and now come to complete the present invention.

Thus the present invention provides aramid thin sheet material useful as separation panels between conductive members of electrical/electronic parts such as condensers, capacitors, batteries and the like, which is characterized by comprising two components of aramid staple fibers and fibrillated aramid, or said two components and aramid fibrid.

The invention also provides above aramid thin sheet material which is characterized by satisfying both of the following expressions (1) and (2): [internal resistance] (μm)≦250 (μm)  expression (1) [Oken-type gas permeability] (sec/100 cm³)≧0.5 (sec/100 cm³)  expression (2)

-   -   wherein the [internal resistance] is a resistance value         calculated by the following expression (3): $\begin{matrix}         {\frac{\begin{matrix}         {{\left\lbrack {{internal}\quad{resistance}}\quad \right\rbrack\left( {\mu\quad m} \right)} =} \\         \begin{bmatrix}         {{{electrical}\quad{conductivity}}\quad} \\         {{of}\quad{electrolyic}\quad{solution}}         \end{bmatrix}         \end{matrix}}{\begin{bmatrix}         \begin{matrix}         {{electrical}\quad{conductivity}} \\         {{of}\quad{electrolytic}}         \end{matrix} \\         {{{solution}\text{-}{injected}}\quad} \\         {{thin}\quad{sheet}\quad{material}}         \end{bmatrix}} \times \begin{bmatrix}         {{thickness}\quad} \\         {{{of}\quad{the}}\quad} \\         {\quad{thinsheet}} \\         {\quad{material}}         \end{bmatrix}{\left( {\mu\quad m} \right).}} & {{expression}\quad(3)}         \end{matrix}$     -   wherein [electrical conductivity of electrolytic         solution-injected thin sheet material] is the electrical         conductivity calculated from an AC impedance measured by         sandwiching the electrolytic solution-injected thin sheet         material between two electrodes.

This invention also provides electrical/electronic parts such as condensers, capacitors, batteries and the like, characterized by using the aramid thin sheet material of the present invention as separator panels between their electrically conductive members.

Hereinafter the present invention is explained in further details.

(Aramid)

In the present invention, “aramid” signifies a linear high molecular weight compound in which at least 60% of amide linkages directly bind to aromatic ring. As such aramid, for example, polymetaphenylene isophthalamide and copolymers thereof, polyparaphenylene terephthalamide and copolymers thereof, poly(paraphenylene)-copoly(3,4-diphenylether)terephthalamide and the like can be named. These aramids are industrially manufactured by known interfacial polymerization, solution polymerization or the like using, for example, isophthalic acid chloride and mataphenylenediamine and are available on the market, but are not limited thereto. Of these aramids, polymetaphenylene isophthalamide is used with preference, because of its favorable shaping processability, heat-adherability, flame resistance and heat resistance properties.

(Aramid Fibrid)

In the present invention, “aramid fibrid” signify filmy aramid particles having paper-forming ability, which are also referred to as aramid pulp (see: JP Sho 35(1960)-11851B, JP Sho 37(1962)-5752B).

It is widely known that aramid fibrid is useful as paper-forming material, after maceration and beating treatment, similarly to ordinary wood pulp. With the view to maintain the quality adequate for paper-forming, aramid fibrid can be given a “beating” treatment. This beating treatment can be worked with disc refiner, beater, or other paper-forming material processing machine or instrument which exerts mechanical cutting action. In such operation, morphological change in the fibrid can be monitored by freeness test method prescribed by The Japanese Industrial Standards P8121.

In the present invention, freeness of the aramid fibrid after the beating treatment preferably lies within a range of 10-300 cm³, in particular, 10-80 cm³ (Canadian freeness). With fibrid having the freeness more than the specified range, the aramid thin sheet material formed therefrom is liable to have reduced strength. On the other hand, attempts to achieve freeness less than 10 cm³ reduce utilization efficiency of mechanical power projected and often decrease processing quantity per unit time. Furthermore, because such excessively advances pulverization of the fibrid, it is apt to invite deterioration in “binder” function. Hence, no substantial merit is found in attempts to obtain freeness less than 10 cm³.

For the utility intended in the present invention, aramid fibrid preferably has a weight-average fiber length after the beating treatment, as measured with optical fiber length measuring apparatus, not more than 1.5 mm, in particular, within a range of 1.2-0.6 mm. As the optical fiber length measuring apparatus, Fiber Quality Analyzer (Op Test Equipment Co.), KAJAANI Measuring Equipment (Kajaani Co.) or the like can be used. With such an equipment, fiber length and form of aramid fibrid passing a certain light path are observed individually and the measured fiber lengths are statistically processed. Where the weight-average fiber length of the aramid fibrid to be used exceeds 1 mm, reduction in electrolytic solution absorbency, occurrence of localized failure of impregnation with the electrolyte, and consequential rise in internal resistance of electrical/electronic parts are liable to take place.

(Aramid Staple Fiber)

Aramid staple fiber is provided by cutting fibers of which starting material is aramid, examples of which include those available under the tradenames of Teijin CONEX® (Teijin Ltd.), TECHNORA® (Teijin Ltd.), APIER® (UNITIKA Ltd.) NOMEX® and KEVLAR® (E. I. du Pont de Nemours and Company) and TWARON® (Teijin Twaron Co.), but not limited thereto.

Aramid staple fiber preferably has a fineness within a range of 0.05 dtex-less than 25 dtex, in particular, 0.1-2 dtex. Here the fineness is defined as fiber weight (g) per 1000 m. Fibers having a fineness less than 0.05 dtex are objectionable as they tend to invite agglomeration during wet process preparation (explained later), and fibers having a fineness of 25 dtex or more tend to have excessively large fiber diameter. For example, where the fibers have a round cross-section and have a density of 1.4 g/cm³, fibers having a diameter of 45μ or more are liable to cause such defects as decrease in aspect ratio, reduction in mechanical reinforcing effect, non-uniformity of aramid thin sheet material or the like. Here non-uniformity of aramid thin sheet material signifies broadening in void size distribution to cause non-uniformity in mobility of aforesaid ion species.

The length of aramid staple fibers can be selected between 1 mm to less than 50 mm, in particular, 2-10 mm. Where the length of the staple fibers is less than 1 mm, mechanical characteristics of aramid thin sheet material are deteriorated, and when it is 50 mm or more, tangle or stuck is apt to take place during preparation of aramid thin sheet material by later described wet process to induce further defects.

(Fibrillated Aramid)

Fibrillated aramid is formed by fibrillating aramid fibers, aramid fibrid and the like by exertion of shearing force, which preferably has a freeness within a range of 10-800 cm³, in particular, 30-700 cm³ (Canadian freeness). Fibrillated aramid having a freeness greater than the above range is liable to provide insufficient shielding property between electrodes. On the other hand, attempts to obtain the freeness less than 10 cm³ excessively advance fineness of fibrillated aramid, which is apt to invite deterioration in its binder function. Therefore, no particular merit is found in achieving a freeness less than 10 cm³.

Fibrillated aramid preferably has a specific surface area of at least 5 g/m², in particular, 6-20 g/m². When it is less than 5 g/m², reduction in binder function is apt to be invited. Furthermore, its weight-average fiber length can be selected from a range of 0.01 mm-less than 7 mm, in particular, 0.3-3 mm. Fibrillated aramid having greater weight-average fiber length than the specified range shows poor dispersibility during paper-forming operation, which may cause local defect in formed aramid thin sheet material such as formation of stuck filament. On the other hand, attempts to obtain weight-average fiber length less than 0.01 mm promote excessive pulverization of fibrillated aramid and are liable to invite reduction in its binder function.

Specific examples of fibrillated aramid are available under such tradenames as KEVLAR PULP (E. I. du Pont de Nemours and Company), TWARON PULP (Teijin Twaron Co.) and the like, but are not limited thereto.

(Aramid Thin Sheet Material)

The aramid thin sheet material of the present invention is characterized by being constituted of the two components, i.e., above-described aramid staple fibers and fibrillated aramid, or of the two components plus aramid fibrid, and can have optional aramid staple fiber content, fibrillated aramid content, aramid fibrid content, basis weight and density (basis weight/thickness) within the range satisfying the following two expressions (1) and (2): [internal resistance] (μm)≦250 (μm)  expression (1) [Oken-type gas permeability] (sec/100 cm³)≧0.5 (sec/100 cm³)  expression (2) preferably [internal resistance] (μm)≦230 (μm)  expression (1) [Oken-type gas permeability] (sec/100 cm³)≧1 (sec/100 cm³)  expression (2)

-   -   wherein the [internal resistance] (μm) is a resistance         calculated by the following expression (3): $\begin{matrix}         {\frac{\begin{matrix}         {{\left\lbrack {{internal}\quad{resistance}}\quad \right\rbrack\left( {\mu\quad m} \right)} =} \\         \begin{bmatrix}         {{{electrical}\quad{conductivity}}\quad} \\         {{of}\quad{electrolyic}\quad{solution}}         \end{bmatrix}         \end{matrix}}{\begin{bmatrix}         \begin{matrix}         {{electrical}\quad{conductivity}} \\         {{of}\quad{electrolytic}}         \end{matrix} \\         {{{solution}\text{-}{injected}}\quad} \\         {{thin}\quad{sheet}\quad{material}}         \end{bmatrix}} \times \begin{bmatrix}         {{thickness}\quad} \\         {{{of}\quad{the}}\quad} \\         {\quad{thinsheet}} \\         {\quad{material}}         \end{bmatrix}{\left( {\mu\quad m} \right).}} & {{expression}\quad(3)}         \end{matrix}$     -   said [electrical donductivity of electrolytic solution-injected         thin sheet material] being the electrical conductivity         calculated from AC impedance measured by sandwiching the         electrolytic solution-injected thin sheet material between two         electrodes.         Generally preferred aramid staple fiber content is within a         range of 20-80%, in particular, 30-70%. When the thin sheet         material contains more aramid staple fibers than this range,         binder component becomes insufficient and the paper-forming may         become difficult. On the other hand, the aramid staple fiber         content of less than 20% is liable to cause reduction in         electrolytic solution absorbence, local occurrence of areas not         impregnated with the electrolytic solution and furthermore rise         in internal resistance of electrical/electronic parts.

As to the contents of the components other than aramid staple fibers, it is generally preferred that the fibrillated aramid content is more than that of aramid fibrid. Where aramid fibrid content is increased, the thin sheet material is liable to show reduction in electrolytic solution absorbence, local occurrence of areas not impregnated with the electrolytic solution, and furthermore rise in internal resistance of the electrical/electronic parts using the thin sheet material as separators.

Again, the aramid thin sheet material preferably has a thickness generally within a range of 5 μm-150 μm, in particular, 5 μm-60 μm. Where the thickness is less than 5 μm, the thin sheet material shows reduced mechanical properties and is apt to cause problems in handlability such as retention of separator shape, transportation in production steps and the like. On the other hand, the thickness exceeding 150 μm tends to invite increase in internal resistance and, above all, makes it difficult to produce small-size high performance electrical/electronic parts.

Furthermore, the aramid thin sheet material can generally have a basis weight within a range of 5-150 g/m², in particular, 5-50 g/m². Where the basis weight is less than 5 g/m², the thin sheet material shows insufficient mechanical strength and is apt to cause breakage during the various handling in the parts-manufacturing steps such as impregnation treatment with electrolyte, winding-up and the like. On the other hand, aramid thin sheet material having a basis weight more than 150 g/m² has increased thickness and tends to cause insufficient impregnation with, or infiltration of, electrolyte.

Density of aramid thin sheet material is calculated from basis weight/thickness, which may be normally within a range of 0.1-1.2 g/m³, in particular, 0.1-1.0 g/m³.

Aramid thin sheet materials failing to satisfy the expressions (1) and (2) are liable to cause such troubles as (1) excessive increase in internal resistance of electrical/electronic parts to interfere with their normal actions, (2) failure to maintain shielding performance between electrodes to induce short circuit, when compressed as being sandwiched between electrodes filled at high density.

(Production Method of Aramid Thin Sheet Material)

The aramid thin sheet material of the present invention, which has the characteristic features as described in the foregoing, can be generally prepared by mixing above-described aramid stable fibers with fibrillated aramid, or aramid staple fibers with fibrillated aramid and aramid fibrid at desired ratios, and thereafter sheeting the mixture. More specifically, for example, such a method comprising dry-blending above aramid staple fibers with fibrillated aramid, or aramid staple fibers with fibrillated aramid and aramid fibrid, and thereafter forming a sheet thereof utilizing gaseous current; one comprising dispersing and mixing aramid staple fibers with fibrillated aramid, or aramid staple fibers with fibrillated aramid and aramid fibrid, in a liquid medium, and thereafter discharging the mixture on a liquid-permeable support, e.g., net or belt for sheeting, whereby removing the liquid and drying the residue; or the like can be applied. Of these, one normally referred to as wet paper-forming method which uses water as the medium is preferred.

Such a wet paper-forming method is generally practiced by feeding an aqueous slurry of a two- or three-component mixture containing at least aramid staple fibers and fibrillated aramid, or aramid staple fibers, fibrillated aramid and aramid fibrid, to a paper machine and dispersing the same; de-watering, squeezing, drying to convert it into a sheet form and taking it up. As the paper machine, Fourdrinier machine, cylinder paper machine, inclined paper machine or combination paper machine combining those can be used. In the preparation using a combination paper machine, composite sheet composed of plural paper layers can be obtained by sheet-forming slurries of differing blend ratios and integrating them. In the occasion of paper-forming, additives such as dispersibility improving agent, defoaming agent, strength-enhancing agent and the like may be added, where necessary. Besides such additives, other fibrous components (e.g., organic fibers such as polyphenylene sulfide fibers, polyester ether ketone fibers, cellulose fibers, PVA fibers, polyester fibers, acrylate fibers, liquid crystalline polyester fibers, polyethylene naphthalate fibers and the like; inorganic fibers such as glass fibers, rock wool, asbestos, boron fibers and the like) may also be added. Where such other fibrous component(s) are added, their preferred blend ratio is 10% or less, based on the total weight of all of the fiber components.

So obtained aramid thin sheet material can be imparted with increased density and mechanical strength by, for example, hot-pressing it at high temperature and high pressure as sandwiched between a pair of flat plates or metal rolls. The hot-pressing conditions can be, for example, where metallic rolls are used, 100-400° C. in temperature range and 50-400 kg/cm in linear pressure range, but are not limited thereto. The material may also be simply pressed at ambient temperature, without the heating treatment. In the procedure of hot-pressing, plural sheets of the thin sheet material may be laminated. The hot-press processing may be repeated optional number of times by an optional order.

The aramid thin sheet material of the present invention can be used as laminated with known other separator (e.g., polyolefine microporous membrane) by per se known means (e.g., above hot-press processing) for further increasing its strength.

The aramid thin sheet material of the present invention can be favorably used as separator panels in electrical/electronic parts, because of (1) its excellent properties such as heat resistance and flame resistance; (2) excellent electrolyte-retaining function attributable to its void structure; and (3) aramid's light weight as demonstrated by its low specific density of around 1.4.

Thus, electrical/electronic parts such as condensers, capacitors and batteries manufactured with use of the aramid thin sheet material of the present invention as separator panels between electrically conductive members show high shielding property between electrodes and maintain high safety. Also due to the material's inherently high heat resistance, the electrical/electronic parts achieve the effect of withstanding the use under heavy current environment of hybrid cars, electric cars and the like.

(Internal Resistance)

The [internal resistance] which characterizes the aramid thin sheet material of the present invention is the resistance which is calculated according to the following expression (3): $\begin{matrix} {\frac{\begin{matrix} {{\left\lbrack {{internal}\quad{resistance}}\quad \right\rbrack\left( {\mu\quad m} \right)} =} \\ \begin{bmatrix} {{{electrical}\quad{conductivity}}\quad} \\ {{of}\quad{electrolyic}\quad{solution}} \end{bmatrix} \end{matrix}}{\begin{bmatrix} \begin{matrix} {{electrical}\quad{conductivity}} \\ {{of}\quad{electrolytic}} \end{matrix} \\ {{{solution}\text{-}{injected}}\quad} \\ {{thin}\quad{sheet}\quad{material}} \end{bmatrix}} \times \begin{bmatrix} {{thickness}\quad} \\ {{{of}\quad{the}}\quad} \\ {\quad{thinsheet}} \\ {\quad{material}} \end{bmatrix}{\left( {\mu\quad m} \right).}} & {{expression}\quad(3)} \end{matrix}$

-   -   said [electrical donductivity of electrolytic solution-injected         thin sheet material] being the electrical conductivity         calculated from AC impedance measured by sandwiching the         electrolytic solution-injected thin sheet material between two         electrodes.

Here the “electrolytic solution” signifies a liquid formed by dissolving an electrolyte in a solvent.

In the present invention, kinds of solvent and electrolyte useful for the electrolytic solution and concentration of the electrolyte are subject to no particular limitation. As examples of the solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, butylene carbonate, glutaronitrile, adiponitrile, acetonitrile, methoxyacetonitrile, 3-methoxypropionitrile, γ-butyrolactone, γ-valerolactone, sulfolane, 3-methylsulfolane, nitroethane, nitromethane, trimethyl phosphate, N-methyloxazolidinone, N,N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, N,N′-dimethylimidazolidinone, amidine, water, and mixtures of two or more of the foregoing can be named.

Electrolyte includes ionic substances, and as the ionic components of the substances, for example, following combinations of cations with anions can be named:

1) cation; quaternary ammonium ion, quaternary phosphonium ion, lithium ion, sodium ion, ammonium ion, hydrogen ion and mixtures of the foregoing

2) anion; perchlorate ion, borofluoride ion, hexafluorophosphate ion, sulfate ion, hydroxide ion and mixtures of the foregoing.

(Electrical conductivity of electrolytic solution-injected thin sheet material) in the present invention is the electrical conductivity calculated from AC impedance as measured by sandwiching the electrolytic solution-injected thin sheet material between two electrodes. Measuring frequency for the AC impedance is not critical, but the normally preferred range is 1 kHz-100 kHz.

EXAMPLES

Hereinafter the present invention is explained more specifically, referring to working examples. It should be understood, however, these examples are for illustration only and are never for restricting the scope of the present invention.

<Measuring Methods>

(1) BW (Basis Weight) and Thickness Measurement of Sheet

Those methods as prescribed by JIS C2111 were followed.

(2) Measurement of Electrical Conductivity

A disc of 20 mm in diameter was cut out from a thin sheet material, which was sandwiched between two sheets of SUS electrodes and AC impedance at 60 kHz was measured as the basis for the conductivity calculation. The measuring temperature was 25° C. For the measurement, 1M lithium borofluoride solution in ethylene carbonate/propylene carbonate (1:1 by weight) was used as the electrolytic solution.

(3) Gas Permeability

Gas permeability was measured with Oken-type gas permeability meter. As to all of the thin sheet materials measured in the present invention, the less this time, the more porous the material.

(Preparation of Starting Materials)

By the method using a wet precipitation machine composed of stator/rotor combination as described in JP Sho52(1977)-151624B, fibrid of polymetaphenylene isophthalamide was prepared, which was processed with macerator and beater to adjust its weight-average fiber length to 0.9 mm.

Separately, metaramid fibers (Teijin CONEX®, Teijin Ltd.) having a staple fineness of 0.8 denier) were cut into 5 mm in length. Also TWARON pulp (TWARON®, Teijin Twaron Co.) was processed to have a specific surface area of 14 m²/g and a freeness of 85 mL; and polyester staple fibers (TETORON®, Teijin Ltd., staple fineness=0.1 denier) were cut to 5 mm in length. Those were used as the starting materials for paper-forming.

Examples 1 and 2

(Preparation of Aramid Thin Sheet Material)

Each of the aramid fibrid, aramid staple fibers and fibrillated aramid prepared in the foregoing manner was dispersed in water to form a slurry. Those slurries were mixed to make the blend ratios of the aramid fibrid, aramid staple fibers and fibrillated aramid the values as indicated in Table 1, to form sheet-formed products with TAPPI sheet machine (cross-sectional area=325 cm²). The products were then given a hot-press processing with metallic calendar rolls at a temperature of 330° C. and linear pressure of 100 kg/cm to provide thin sheet materials.

Main parameter values of thus obtained aramid thin sheet materials were as shown in Table 1. TABLE 1 Physical Property Unit Example 1 Example 2 Composition of starting material wt % Aramid fibrid 0 1 Aramid staple fiber 50 49 Fibrillated aramid 50 50 Basis weight g/m² 24.5 24.4 Thickness μm 51 47 Density g/cm³ 0.48 0.52 Electrical conductivity mS/cm 1.37 1.04 Internal resistance μm 186 245 Gas permeability sec/100 cm³ 1.8 4.8

Electrical conductivity of the electrolytic solution was 5.0 (mS/cm).

The aramid thin sheet materials of those Examples had sufficiently low internal resistance, exhibited satisfactory ion species' permeability and gas permeability, and were considered to be fully capable of maintaining shielding property between electrodes. Accordingly, the products are useful as separator panels of electrically conductive members in electrical/electronic parts such as condensers, capacitors, batteries and the like.

Comparative Example 1

(Preparation of Thin Sheet Material)

Each of the aramid fibrid, aramid staple fibers and TETORON staple fibers as prepared in the foregoing manner was dispersed in water to form a slurry. The slurries were mixed to make the blend ratio of the fibrid and aramid staple fibers the value as indicated in Table 2, to form a sheet-formed product by wet paper-forming method.

The product was then given a hot-press processing with metallic calendar rolls at a temperature of 230° C. and linear pressure of 300 kg/cm to provide a thin sheet material.

Main parameter values of thus obtained thin sheet material were as shown in Table 2. TABLE 2 Comparative Physical Property Unit Example Composition of starting material wt % Aramid fibrid 7 Aramid staple fiber 10 Polyester staple fiber 83 Basis weight g/m² 25 Thickness μm 42 Density g/cm³ 0.6 Electrical conductivity mS/cm 0.60 Internal resistance μm 350 Gas permeability sec/100 cm³ 72

Electrical conductivity of the electrolytic solution was 5.0 (mS/cm).

The thin sheet material of Comparative Example had a high internal resistance and was considered to have insufficient ion species' permeability. Furthermore, because polyester staple fiber was used, the product would not withstand high temperature drying.

Industrial Applicability

The aramid thin sheet material of the present invention can fully maintain shielding property between electrodes and exhibit satisfactory permeability for ion species, and therefore are useful as separator panels for electrically conductive members in electrical/electronic parts such as condensers, capacitors, batteries and the like. Furthermore, the electrical/electronic parts such as condensers, capacitors, batteries and the like in which the aramid thin sheet material of the present invention is used can be dried at high temperatures concurrently with microporous aluminum foil electrodes, active carbon electrodes and the like integrated therein during their manufacturing steps, accomplishing the effect that no deletrious influence of residual moisture on electrical characteristics of the electrical/electronic parts is observed. 

1. An aramid thin sheet material comprising two components of aramid staple fibers and fibrillated aramid, or said two components and aramid fibrid.
 2. An aramid thin sheet material as set forth in claim 1, characterized by satisfying both of the following expressions (1) and (2): [internal resistance] (μm)≦250 (μm)  expression (1) [Oken-type gas permeability] (sec/100 cm³)≧0.5 (sec/100 cm³)  expression (2) wherein the [internal resistance] is a resistance value calculated by the following expression (3): $\begin{matrix} {\frac{\begin{matrix} {{\left\lbrack {{internal}\quad{resistance}}\quad \right\rbrack\left( {\mu\quad m} \right)} =} \\ \begin{bmatrix} {{{electrical}\quad{conductivity}}\quad} \\ {{of}\quad{electrolyic}\quad{solution}} \end{bmatrix} \end{matrix}}{\begin{bmatrix} \begin{matrix} {{electrical}\quad{conductivity}} \\ {{of}\quad{electrolytic}} \end{matrix} \\ {{{solution}\text{-}{injected}}\quad} \\ {{thin}\quad{sheet}\quad{material}} \end{bmatrix}} \times \begin{bmatrix} {{thickness}\quad} \\ {{{of}\quad{the}}\quad} \\ {\quad{thinsheet}} \\ {\quad{material}} \end{bmatrix}{\left( {\mu\quad m} \right).}} & {{expression}\quad(3)} \end{matrix}$ wherein [electrical conductivity of electrolytic solution-injected thin sheet material] is the electrical conductivity calculated from an AC impedance measured by sandwiching the electrolytic solution-injected thin sheet material between two electrodes.
 3. Electrical/electronic parts which are characterized by using the aramid thin sheet material as set forth in claim 1 or 2 as separator panels between their electrically conductive members. 